Rework examine_opclause_expression to use varonleft

The examine_opclause_expression function needs to return information on
which side of the operator we found the Var, but the variable was called
"isgt" which is rather misleading (it assumes the operator is either
less-than or greater-than, but it may be equality or something else).
Other places in the planner use a variable called "varonleft" for this
purpose, so just adopt the same convention here.

The code also assumed we don't care about this flag for equality, as
(Var = Const) and (Const = Var) should be the same thing. But that does
not work for cross-type operators, in which case we need to pass the
parameters to the procedure in the right order. So just use the same
code for all types of expressions.

This means we don't need to care about the selectivity estimation
function anymore, at least not in this code. We should only get the
supported cases here (thanks to statext_is_compatible_clause).

Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/8736jdhbhc.fsf%40ansel.ydns.eu
Backpatch-to: 12

1 files changed, 8 insertions, 8 deletions

diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c
index d2346cbe02e..23c74f7d90a 100644
--- a/src/backend/statistics/extended_stats.c
+++ b/src/backend/statistics/extended_stats.c
@@ -1196,15 +1196,15 @@ statext_clauselist_selectivity(PlannerInfo *root, List *clauses, int varRelid,
  * returns true, otherwise returns false.
  *
  * Optionally returns pointers to the extracted Var/Const nodes, when passed
- * non-null pointers (varp, cstp and isgtp). The isgt flag specifies whether
- * the Var node is on the left (false) or right (true) side of the operator.
+ * non-null pointers (varp, cstp and varonleftp). The varonleftp flag specifies
+ * on which side of the operator we found the Var node.
  */
 bool
-examine_opclause_expression(OpExpr *expr, Var **varp, Const **cstp, bool *isgtp)
+examine_opclause_expression(OpExpr *expr, Var **varp, Const **cstp, bool *varonleftp)
 {
 	Var	   *var;
 	Const  *cst;
-	bool	isgt;
+	bool	varonleft;
 	Node   *leftop,
 		   *rightop;
 
@@ -1225,13 +1225,13 @@ examine_opclause_expression(OpExpr *expr, Var **varp, Const **cstp, bool *isgtp)
 	{
 		var = (Var *) leftop;
 		cst = (Const *) rightop;
-		isgt = false;
+		varonleft = true;
 	}
 	else if (IsA(leftop, Const) && IsA(rightop, Var))
 	{
 		var = (Var *) rightop;
 		cst = (Const *) leftop;
-		isgt = true;
+		varonleft = false;
 	}
 	else
 		return false;
@@ -1243,8 +1243,8 @@ examine_opclause_expression(OpExpr *expr, Var **varp, Const **cstp, bool *isgtp)
 	if (cstp)
 		*cstp = cst;
 
-	if (isgtp)
-		*isgtp = isgt;
+	if (varonleftp)
+		*varonleftp = varonleft;
 
 	return true;
 }